Well, I am an old guy in this game, and I guess things have changed to the better. When I started i rc in 77-78 we only used FAI fuel without nitro and only plain castor oil, and had no problems with rust and corrosion, but had to preserve the engines with after run oil if the engines where not to be used for months or more or as the castor would gum and seize the bearings.
In my rc-car racing time, we used 25% nitro and 10% castor oil that we usually blended by ourselfes. And this could not be left even overnight without rust taking place. We either had to run the engines after the days racing with plain 0% nitro fuel, or flush the engines with 5-56/WD-40 and running it through on the starter.
A few years ago, about 4 years i think, I got myself an O.S. 200 fourstroke engine. Due to servo failure the plane and engine went down very hard, totally destroying the plane and major damage to the engine. I was told by the supplier of the fuel that I was using, about 15% nitro, had additives to prevent rust and corrosion, so I didn't have to think about preserving the engine while I was getting new parts for it. Well, when I took it apart some months later, it was totally corroded inside, and it went in the trash. So much for modern fuel 4 years ago.
To this day I have never seen a nitrofuel that is corrosionproof, and I have my doubts if I ever will. Methanole attracts water, and nitro leaves very corrosive remains in the engine. This is a sure recipy for corrosion that is very difficult to avoid.
